The present invention relates to the machining of turbine bucket covers, and, more particularly, to the reduction of burr formation during the machining of turbine bucket covers.
A turbine assembly is formed by securing a plurality of turbine blades or buckets to a turbine rotor wheel. The buckets have covers formed at their radial ends. The covers are machined to a desired profile to form sealing teeth that line up with similarly configured teeth on spill strips, thereby improving the efficiency of the turbine unit. This machining of the bucket covers introduces burrs into the gaps between adjacent bucket covers. These burrs have been found to cause frequency shifts that may reach as high as 12%. Such frequency shifts can cause excessive vibration during turbine operation, leading to metal fatigue and possibly failure. To remove the burrs, the turbine must be disassembled and the burrs are then ground down. Once the burrs have been removed, the turbine must be reassembled. This process is extremely time consuming, and, consequently, very expensive.
There is a need to provide a method of machining turbine bucket covers that reduces or wholly overcomes some or all of the difficulties inherent in prior known methods. Particular objects and advantages of the invention will be apparent to those skilled in the art, that is, those who are knowledgeable or experienced in this field of technology, in view of the following disclosure of the invention and detailed description of preferred embodiments.
It is, therefore, seen to be desirable to provide a method of machining turbine bucket covers that reduces the formation of burrs during the machining operation, while not requiring the disassembly and reassembly of the turbine in order to do so.
In accordance with a first aspect, a method of reducing the formation of burrs during machining of turbine bucket covers of a turbine assembly includes the steps of inserting a filler material in a gap formed between adjacent bucket covers of a turbine assembly, machining the bucket covers to produce a desired profile for the bucket covers, and removing the filler material.
In accordance with another aspect, a method of reducing the formation of burrs during machining of turbine bucket covers of a turbine assembly includes the steps of providing a plurality of buckets with bucket covers about a rotor wheel, where the buckets extend radially outward from the rotor wheel, each bucket cover has a contact surface to engage in an interfering fit relationship with a contact surface of an adjacent bucket cover and axially extending surfaces on either side of the contact surface, and leading edge and trailing edge gaps are formed between respective axially extending surfaces of adjacent bucket covers; inserting a filler material in each leading edge gap and each trailing edge gap; machining the bucket covers to a desired profile; and removing the filler material.
In accordance with yet another aspect, a method of reducing the formation of burrs during machining of bucket covers of a turbine assembly includes the steps of providing a turbine having a rotor wheel; securing a plurality of buckets about a circumference of the rotor wheel, with each bucket having a cover including an axial contact surface to engage in interfering fit relationship with an axial contact surface of an adjacent bucket cover and axially extending surfaces on either side of the axial contact surface, wherein leading edge and trailing edge gaps are formed between respective axially extending surfaces of adjacent bucket covers; inserting a filler material in each leading edge gap and each trailing edge gap; machining the bucket covers to a desired profile; and removing the filler material.
From the foregoing disclosure, it will be readily apparent to those skilled in the art that the present invention provides a significant advance. Preferred embodiments of the method of the present invention can provide significant reduction in the formation of burrs during machining of turbine bucket covers, thereby saving numerous hours that would otherwise be required to disassemble the buckets and manually remove the burrs. This presents a significant cost savings in the assembly of turbines. These and additional features and advantages of the invention disclosed here will be further understood from the following detailed disclosure of preferred embodiments.